01 - Line a rimmed baking sheet with parchment paper or a silicone baking mat and set aside.
02 - Toast pecan halves in a dry skillet over medium heat for 3 to 4 minutes, stirring frequently, until fragrant and lightly colored. Allow to cool completely, then roughly chop into bite-sized pieces.
03 - In a large heavy-bottomed saucepan, combine the granulated sugar, light corn syrup, and water. Stir continuously over medium heat until the sugar has fully dissolved and the mixture appears clear.
04 - Bring the syrup to a steady simmer and attach a candy thermometer to the side of the pan. Stop stirring and allow the mixture to cook undisturbed until it registers 300°F (hard crack stage), approximately 10 to 12 minutes.
05 - Remove the saucepan from heat. Working quickly, add the unsalted butter, vanilla extract, sea salt, baking soda, chopped pecans, and puffed quinoa. Stir vigorously and thoroughly to combine — the mixture will bubble and foam as the baking soda reacts.
06 - Immediately pour the hot mixture onto the prepared baking sheet. Using a heatproof spatula, spread it out evenly to approximately 1/4-inch thickness, working fast before it begins to set.
07 - Sprinkle the surface generously with additional flaky sea salt while still warm. Allow the brittle to cool undisturbed at room temperature for at least 30 minutes, or until completely hardened and set.
08 - Once fully cooled and firm, break the brittle into 12 irregular pieces by hand or tap gently with a knife handle. Serve immediately or store for later.